A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus are conventionally used, for example, in the manufacture of integrated circuits (ICs), flat panel displays and other devices involving fine structures.
It is desirable to reduce the size of features in a lithographic pattern because this allows for a greater density of features on a given substrate area. In photolithography, the increased resolution may be achieved by using light of shorter wavelength. However, there are problems associated with such reductions. Current systems are starting to adopt optical sources with wavelengths in the 193 nm regime but even at this level, diffraction limitations become a barrier. At lower wavelengths, the transparency of materials is very poor. Optical lithography machines capable of enhanced resolutions require complex optics and rare materials and are consequently very expensive.
An alternative for printing sub-100 nm features, known as imprint lithography, includes transferring a pattern to a substrate by imprinting a pattern into an imprintable medium using a physical mold or imprint template. The imprintable medium may be the substrate or a material coated on to a surface of the substrate. The imprintable medium may be functional or may be used as a “mask” to transfer a pattern to an underlying surface. The imprintable medium may for example be provided as a resist deposited on a substrate such as a semiconductor material to which the pattern defined by the imprint template is to be transferred. Imprint lithography is thus essentially a molding process on a micrometer or nanometer scale in which the topography of a imprint template defines the patterns created on a substrate. Patterns may be layered as with optical lithography processes so that in principle imprint lithography could be used for such applications as IC manufacture.
The resolution of imprint lithography is limited only by the resolution of the imprint template fabrication process. For example, imprint lithography has been used to produce features in the sub-50 nm range with significantly improved resolution and line edge roughness compared to that achievable with conventional optical lithography processes. In addition, imprint processes do not require expensive optics, advanced illumination sources or specialised resist materials typically required by optical lithography processes.
Fabrication of imprint templates is typically performed using electron beam lithography, which is generally time consuming and expensive (electron beam lithography machines are expensive to buy and to run).